Automatic control of light flash pulses

ABSTRACT

A device for controlling the termination of light emission by a flash device including means for detecting the light reflected from the subject being illuminated by the flash, integrating means connected to the detecting means for providing a flash termination signal when the total amount of light received by the detecting means reaches a predetermined value, and flash termination means connected to the integrating device and to the flash device for terminating the delivery of electrical energy to the flash device when the signal from the integrating device reaches its predetermined value. The flash termination device is preferably constituted by a novel gas-filled, arc-producing element having identical, unpolarized electrodes and an internal or external triggering electrode.

United States Patent Vital et al.

[ 1 Dec. 24, 1974 AUTOMATIC CONTROL OF LIGHT FLASH PULSES [75]Inventors: Zoltan Vital, Uccle; Jean Orban,

Clabecq, both of Belgium [73] Assignee: Ponder & Best, Inc., LosAngeles,

Calif.

[22] Filed: Apr. 14, 1972 [21] Appl. No.: 244,279

' Related U.S. Application Data [63] Continuation of Ser. No. 799,554,Feb. 13, 1969,

abandoned.

[30] Foreign Application Priority Data Feb. 13, 1968 Belgium 54471 Nov.21, 1968 Belgium 66425 Dec. 27, 1968 Belgium 68017 Jan. 20, 1969 Belgium68982 [52] U.S. Cl. 315/241 P, 315/151, 315/159, 315/241 R [51] Int. Cl.H05b 37/02 [58] Field of Search 315/149, 151,159,241 P, 315/241 R;307/252 B; 323/22 SC [56] References Cited UNITED STATES PATENTS3,525,033 8/1970 Greenberg et al. H 323/22 SC FIRING VOLTAGE SUPPLY3,591,829 7/1971 Murata et al. 315/151 Primary Examiner-Harman KarlSaalbach Assistant ExaminerLawrence J. Dahl Attorney, Agent, orFirmSpencer & Kaye [57] ABSTRACT A device for controlling thetermination of light emission by a flash device including means fordetecting the light reflected from the subject being illuminated by theflash, integrating means connected to the detecting means for providinga flash termination signal when the total amount of light received bythe detecting means reaches a predetermined value, and flash terminationmeans connected to the integrating device and to the flash device forterminating the delivery of electrical energy to the flash device whenthe signal from the integrating device reaches its predetermined value.The flash termination device is preferably constituted by a novelgas-filled, arc-producing element having identical, unpolarizedelectrodes and an internal or external triggering electrode.

VOLTMETER I08? H QE INTEGRATOR suaazcr Patented Deg. 24, 1974 3,857,064

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10/ J04 J07 J11 J08 m/ VENTORS Zolton Vital 8 Jean Orbon A TTORNEYSPatented Dec. 24, 1974 9 Sheets-Sheet 2 COMPENSATING INVENTORS ATTORNEYSCAMERA Ell- SYNCHRONIZING CONTACTS APERTURE DISC Zolton Vitul8 JeanOrbcm Patented Dec. 24, 1974 3,857,064

9 Sheets-Sheet Z 7v VE N TORS Zolton vitala Jean Orbon ATTORNEYSPatented Dec. 24, 1974 3,857,064

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. INVENTORS Zolton Vital 8 Jean Orban BY m am 5 7 67 2 A TTORNEYSPatented Dec. 24, 1974 9 Sheets-Sheet 6 INVENTORS Zoltcm Vitol 8 JeanOrbon AT TORN E YS Patented Dec. 24, 1974 3,857,064

9 Sheets-Sheet 7 PHOTO- EMISSION FIBER LENS MATERIAL F ig. I9

INVENTORS Zdl ton Vital 8 Jean Orbon ATTORNEYS Patented Dec. 24, 1.9743,857,064

9 Sheets-Sheet 8 IN VE N TORS Zolton Vital 8 J an n O rbo n ATTORNEYSPatented Dec. 24, 1974 3,857,064

9 Sheets-Sheet 9 Fig. I8

C9 w i H may INVENTORS Zolton Vitalfi Jean Orbon ATTORNEYS AUTOMATICCONTROL OF LIGHT FLASH PULSES CROSS REFERENCE TO RELATED APPLICATIONThis application is a continuation of application Ser. No. 799,554,filed Feb. 13th, 1969 now abandoned.

BACKGROUND OF THE INVENTION The invention concerns a device, circuit andmethod for controlling the impulses generated by the discharge of acapacitor placed either in series or in parallel with the load and, inthe case of a parallel connection, having no more than one electronicswitch. The invention further concerns a novel switching tube for use assuch switch and having other uses and equipped with at least oneimportant further device or circuit.

The invention is intended above all for application to electronicflashes, stroboscopes and lasers.

Such devices are now only known for effecting such control in anautomatic manner and with the capacitor causing the impulse to bypassthe load. Apparatus of such kind is disclosed in U.S. Pat. No. 3,033,988and is composed of a device which controls the light of a photographicenlarger and in which a gas-discharge switching triode with an externalfiring electrode or a mercury tube is provided as a second switch,always with an impedance of about O.l ohm. Concerning the light sensorof this patent, U.S. Pat. No. 3,350,604 states, at column 3, lines27-32: In order to achieve the high photocell dark impedance with therequired high light sensitivity, the light sensitive element must be aphotomultiplier tube. Such tubes require a rather complex power supply.This results in a package which is sufficiently bulky as to preclude itsuse in portable, camera mounted flash equipment. Another known device ofthe same kind is disclosed in U.S. Pat. No. 3,350,604, which isessentially based on the disclosure of U.S. Pat. No. 3,033,988, andrepresents a modification thereof in that this device makes use of anonreactive light integrator, i.e., one without a capacitor, and thepatent states that the use of this is more advantageous than that of theintegrator of U.S. Pat. No. 3,033,988.

These'known devices, which can only operate in an automatic manner,i.e., by being coupled permanently to a sensor, always have two or moreswitches. The switch of the second U.S. Pat. No. (3,350,604) is a xenongas-filled discharge tube, a variant of the wellknown xenon gasfilledphotoflash tube, equipped with an internal firing electrode and having apressure of about I mm Hg. The internal resistance of this tube ismentioned as being 0.1 ohm.

SUMMARY OF THE INVENTION According to the present invention, an improvedcontrol is achieved by a control device serving to arrest the dischargeof a capacitor, and thus extinguish the flash tube.

A modified embodiment of the invention involves a control device whichis used only to extinguish the flash tube. In this case, we use only oneelectronic switch or a gas-filled switching tube of new design, whichrelies on an arc operation and is thus different from the gas dischargetubes of the two U.S. patents discussed above, and which consumes theresidual electrical energy of the capacitor, not used by the flashtube,the switch then being in a bypass circuit. In addition, we use at leastone important complementary device or circuit, such as a specialelectronic gate, a device for the regulation of the sensitivity, etc.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic circuit diagramof a control circuit according to the invention.

FIG. 2 is a view similar to that of FIG. 1 of another form ofconstruction of a control device according to the invention.

FIG. 3 is a view similar to that of FIG. 1 of a further control deviceaccording to the invention.

FIG. 4 is a view similar to that of FIG. 1 of still another controldevice according to the invention.

FIG. 5 is a schematic circuit diagram of a modified type of controlcircuit according to the invention.

. other embodiment of the modified type of control circuit according tothe invention.

FIG. 9 is a view similar to that of FIG. 5 of a still further embodimentof the modified type of control circuit according to the invention.

FIG. 10 is a view similar to that of FIG. 5 of yet another embodiment ofthe modified type of control circuit according to the invention.

FIG. 1 l is a view similar to that of FIG. 5 of yet a further embodimentof the modified type of control circuit according to the invention.

FIG. 12 is a view similar to that of FIG. 5 of a further embodiment ofthe modified type of control device according to the invention.

FIG. 13 is a view similar to that of FIG. 5 of another embodiment of themodified type of control device according to the invention.

FIG. 14 is a view similar to that of FIG. 5 of a further embodiment ofthe modified type of control device according to the invention.

FIG. 15 is a view similar to that of FIG. 5 of a further I FIG. 20 is anelevational view of one embodiment of a novel arc-operated switchaccording to the invention.

FIG. 20a is a cross-sectional view of the embodiment of FIG. 20.

FIG. 21 is a view similar to that of FIG. 20 of another embodiment ofthe switch according to the invention.

FIG. 21a is a cross-sectional view of the embodiment of FIG. 21.

DESCRIPTION OF THE PREFERRED EMBODIMENTS The invention concerns devicesand circuits for controlling impulses generated by the discharge of acapacitor. These impulses are controlled by components placed in seriesand/or parallel withthe load and including an integrator which receivesthe energy of the impulses. This control device may be operated in amanual and/or an automatic manner. All these devices are combinedpreferably with several other devices and circuits. The invention isespecially related to electronic photoflashes,stroboscopes,.lasers andthe like, the reflected light of which is to be received by a lightsensor whose output signal is to be integrated. When the light sensorhas received a predetermined quantity of light, a threshold amplifierconsisting of a unijunction transistor, a four-layer diode or any othersuitable component and placed after the integrator generates impulseswhich control one or several semiconductor switches and/or one orseveral gas-filled tubes and/or one or several lightning arresterspreferably of the gasfilled type, and/or, most particularly, one orseveral gas-filled arc arresters of special construction to be describedlater in a detailed manner, and/or other similar components.

These components control the electrical supply of a flash tube, theimpedance of which is higher than that of the switch, with or withoutarresting the discharge of the photoflash capacitor. Another essentialelement of this invention is the above-mentioned new type of arcarrester component of the gas-filled type, having an impedance of about0.0] ohm when in its conduction state, fitted with at least twoelectrodes, preferably un polarized and even of identical size, andinternally or externally completed with a firing electrode. This newtype of gas-filled switching tube differs from other gasfilled switchingtubes above all because it functions on the basis of an arc and not as agas-discharge tube of the type used in the prior art. The tube accordingto the present invention has the following advantages over all othergas-filled switching tubes, such as those of the two above-cited U.S.patents: lower impedance; larger range of current intensities andvoltages; higher resistance to overloads; easier firing, and this over amore extended range; lower light emission; possibility of utilization atfaster switching rates; increased ruggedness; extended lifetime, smallersizes; and lower cost.

Furthermore, this new component is suitable for use in fields wherethyratrons and thyristors are presently used or where no convenientcomponent is available.

We remark that our control device, when using only one electronic switchor the gas-filled, arc-operation tube according to the invention isconsiderably smaller than all other similar devices, which is of thegreates importance in the case of portable devices.

We describe the supplementary devices and circuits intended to becombined with the control device.

The control device may be completed by one or scvcral electronic gates.The function of the electronic gate is to conduct current from theelectric supply of the control device only during the period of theflash discharge. The supply current is initiated by the discharge of acapacitor. associated with the electronic gate. This capacitor waspreviously charged by the photoflash discharge capacitor through aresistive, inductive, semiconductor, or other element. The supplyvoltage is controlled by a Zener diode, a gas-filled tube, a capacitor,a resistance, or another element.

It is the electronic gate which starts and maintains this control devicefor the duration of each flash of the photoflash and which sets thecontrol device back to its starting point right after the flash isterminated. Thus, it is not possible for the control device to beactuated by any other source of light.

On the other hand, the control device may be completed with a devicethat regulates its own sensitivity, namely, by an adjustable opticaldevice, such as a diaphragm, a set of filters, or others, placed infront of the light sensor of the control device, or by an adjustableelectric or electronic device, such as fixed and/or variablecapacitances, resistances and inductances.

These controls can be operated manually or else by coupling to a part oraccessory of the camera, such as to the diaphragm, the film cassette,e.g. a coded Kodapak cassette, etc. Of course, in the case of a controlcoupled to the camera, both apparatuses should be constructed together.

The regulating components, being designed to be manipulated by the user,are completed with scales graduated in film sensitivities and/or indiaphragm apertures. The selected positions could be ratcheted orlocked. The components to be manipulated and the scales are preferablyinterchangeable and reversible. This same device could be completed by afocal lengthaperture calculator. This same device and its scales can belighted.

Another mode operation consists of controlling the quantity of lightproduced by the flash tube by a manual regulation of the control deviceof the integrator, without intervention by'a light sensor, i.e., withouttaking into account the quantity of reflected light, based on thecamera-to-subject distance, the film sensitivity, etc. In this case, thelightsensor of the control device is replaced by at least one adjustablecomponent, e.g. the setting element of the threshold amplifier of theintegrator, etc. The controls of this device may be graduated indistance, flash-duration, guide-numbers, etc.

Another control function is a determination of whether the operation ofthe control device was completed or not. This control consists of asuitable electric or electronic circuit or else a light sensor, such asa photosensitive element, etc., or a conductor of visible or nonvisiblelight, such as fiber optics, transparent material, etc., or a heatconductor, i.e., responsive to infrared radiation, used in conjunctionwith a gas-filled switching tube, or'with any other component of thecontrol device havingthe kind of emission as described above.

The control device can be completed with a circuit having an electric orelectronic measuring instrument which allows the light integrator tofunction as a photometer, a chronometer, etc., and thus to executedifferent measurements, such as the amount of light reflected, theduration of the flash, etc.

A photoflash equipped with a control device may be advantageouslycompleted with a compensation device, e.g. an induction coil and/or asuitable circuit, connected in series with the flash tube to modify thedischarge impulses to the flash tube, for instance to slow down thedischarge of the capacitor, which means to reduce the rate of increaseof the current density of the capacitor discharge. FIG. 1 shows thecircuit of an electronic photoflash equipped with a control devicehaving only one switch whose purpose is to arrest the capacitordischarge when a predetermined amount of light has been produced.

The arrangement of such a unit is as follows:

An energy storage capacitor 100 is charged through a voltage source 101.A flash tube 102 of the usual type is connected to the capacitorterminals through a switch 103 which is preferably a gate-turn-outthyristor or thyratron, etc., provided, if necessary, with suitablesupplementary circuitry. A light sensor 104, composed of a photodiode,phototransistor, photoresistance, or other, is connected to anintegrating circuit 105 of any well-known type. A firing circuit 106triggers the firing of the flash tube 102. This device works as follows:

The capacitor 100 having been charged by the source 101, the ionizationof the flash tube 102 is induced by the action of the firing circuit106. The light sensor 104 supplying an instantaneous currentproportional to the illumination on subject 107, to the integratingcircuit 105, the latter, when the total amount of light received by thelight sensor 104 reaches a predetermined value, causes a circuit toswing," thus supplying an impulse to the switch 103 which theninterrupts the discharge of the capacitor 100. A

Thus, the light emission of the flash tube is arrested after producingthe requisite amount of light, without any energy being withdrawn fromthe capacitor other than that used for producing the light, and possiblyfor commutating the circuit.

The arrangement of FIG. 1 may be completed in the following manner: byconnecting a voltmeter 108 to the terminals of the integrator circuit105, which is designed for such a connection, an integrating photometer,or chronometer, can be produced, which device has scales in differentmeasuring units.

Another variant is illustrated in FIG. 2 in which we describe a controldevice connected both in series and parallel with the load and combinedwith a compensating device, capable of also being used with thepreceding embodiment, constituted by an induction coil.

The discharge capacitor 200 is charged through the voltage source 201.The flash tube 202 is connected to the terminals of the capacitor 200through the intermediary of the induction coil 203. A thyratron 204 isconnected in parallel with the flash tube 202. A light sensor 205 iscoupled to the integrating circuit 206, receives reflected light fromsubject 209 and controls the firing electrode 207 of the thyratron 204.A firing circuit 208 acts to fire the flash tube 202. Meter 210 isconnected to circuit 206.

The operation of the circuit of FIG. 2 differs from that of FIG. 1 asfollows:

After reaching the predetermined signal value, the circuit of theintegrator 206 triggers the firing electrode 207 of the thyratron 204 inparallel with the flash tube 202. The induction coil 203 allows for ashort period during which the thyratron is practically in shortcircuit.Consequently, the flash tube 202 has enough time to deionize, and henceto become extinguished.

A modification is illustrated in FIG. 3. This control device is combinedwith both an electronic gate and an optical device of regulation of thesensitivity.

The control device consists of an electronic device 30 which isidentical with the device 50 of FIG. 5, of

the-photoflash unit 31 and of an electronic switch 32.

In this device, a light sensor 301 generates a current proportional tothe reflected light from the subject. This current is integrated by acapacitor 302 to give a voltage proportional to the amount of thereflected light. This voltage is applied to a unijunction transistor 304or to a four-layer diode or to some other element or device which wouldserve as suitable substitute, which develops a positive impulse in theresistance 305 as soon as the threshold swing orswitching level, of thiscomponent 304 has been reached.

This impulse is conducted by the capacitor 306 to open a semiconductorswitch, or other gate element, 308 by means of its firing circuit whichcontrols the electronic switch 32 so as to terminate the capacitordischarge and thereby extinguish the flash tube of the photoflash 31. I

As soon as the cycle is ended, the voltage across a resistance 303 setsthe system back to its initial condition. A resistance 307 prevents apremature opening of the semiconductor switch 308. The unit 31 containsthe elements of the photoflash which are not individually referenced.The electronic device 30 contains as its principal element asemiconductor switch, such as a thyristor (SCR), or else a gas-filledswitching tube, preferably of the arc arrester type or a special arcarrester, or another suitable component.

An improvement of the flash control device consists in equipping thisdevice with a voltage applying circuit for the reflected light sensorcircuit.

FIG. 3 also illustrates this circuit arrangement. When the flash tube isfired, the voltage at the flash tube terminals decreases sharply. Thisresults in a current in the circuit of the capacitor 309, the resistance310 and the diode 311. A voltage equal to that across the zener diodeappears at the terminals of the light sensor circuit so as to place itin operation. The current intensity depends on the resistance value ofresistor 310. The period voltage is applied to the light sensor circuitis on the value of the capacitor 309.

The regulation of the sensitivity of the control device is effected bythe user with the help of an adjustable optical device 315 composed of adiaphragm, a set of filters, or others, placed in front of the lightsensor301 of the control device.

A further explanation is given with reference to FIG. 4 which shows alight control device for the flash of an electronic photoflash,consisting of the electronic device 40, which is similar to the device30 of FIG. 3 and the device 50 of FIG. 5 and which is therefore onlypartially shown, of the photoflash 41, which is similar to the device31, and of an electronic switch 42, which is similar to the device 32,connected in series with the flash tube circuit.

This device and its operation are essentially identical to thosedescribed and illustrated previously, namely:

The thyristor 421, which is tired upon closing of the camerasynchronization contacts,applied the voltage of the discharge capacitor411 across the flash tube 412, the latter having received previously afraction of this voltage, the value of which fraction is determined bythe resistances 404 and 423, and to the tube firing circuit consistingof a capacitor 413 and a transformer 414, thus firing the flash. Whenthe thyristor 401 becomes conductive due to the subject having beensufficiently illuminated, it discharges the capacitor 402, which waspreviously charged, into the thyristor 421, which results in reversingthe anode voltage of the thyristor for a short period so as to cause itto block and thus arrest the'discharge of the capacitor 411. Thecapacitance value of the capacitor 402 is selected so as to obtain animpulse of sufficient duration to allow the extinction, or blocking, ofthe thyristor 421. The capacitance value of the capacitor 422 isselected so as to obtain the shortest possible impulse so that theextinction of the thyristor 421 may occur as rapidly as possible. Theresistances 424 and 425 are used to polarize the capacitor 422. Thevalue of resistance 403 must be selected in order to give a currentlower than the maintenance current of the thyristor 401 so as to preventthe capacitor 411 from continuing to discharge itself through thethyristor 401. A compensation device, such as an induction coil, 415modifies the discharge impulse in the flash tube. Among other things, itlengthens the discharge duration, etc.

FIG. shows a control device combined with an electronic gate and with anoptical device for the regulation of sensitivity. This control deviceconsists of an electronic device 50 and the photoflash 51.

The components and operation of this device are identical to thosedescribed with reference to FIG. 3, with the difference that an impulsetransmitted by the capacitor 506 opens a semi-conductor switch, or aspecial arc arrester, etc., 508, via its firing circuit and therebyextinguishes the flash tube 512 of the photoflash while discharging thecapacitor 513 of the latter.

In FIG. 6, we describe another embodiment equipped with a special arcarrester combined with an electronic gate and with an electric devicehaving several capacitors for the regulation of sensitivity. A specialarc arrester 611 and its firing device, which consists of thethyristor606, the resistances 607 and 608, the capacitor 609 and-thetransformer 610, serve as a substitute for the thyristor 508 of FIG. 5.Here, we make use of an electric circuit for adjusting the sensitivity,the circuit consisting of a switch 615 connected to select one of thecapacitors 603 and 604 having different capacitance values.

In FIG. 7 there is shown another embodiment in which the photodiode isreplaced by a phototransistor 702 in order to give a higher sensitivityto the light integrator than .is possible with the photodiode. In FIG. 8the photodiode 802 has an amplification circuit composed essentially ofan npn transistor 803 which allows the selection of a very highsensitivity, as a function of the gain of the transistor.

In FIG. 9 a pnp transistor 903 replaces the npn transistor.

In FIG. 10 the light sensor is a photovoltaic cell, such adjusted byselecting suitable values for the resistances 1215 and 1203.

In FIG. 13 we use a circuit with a four-layer diode constituting aunilateral, bilateral switch, etc. as the level detector and at the sametime as the firing impulse generator for the thyristor 1306.

In FIG. 14 the control device contains a voltage divider circuit whichconsists of the capacitors 1401 and 1403 instead of a Zener diode, acapacitor and a resistance as in the previous arrangements.

In FIG. 15 the control circuit contains a phototransistor 1502 and anelectric device for regulating the sensitivity. The latter deviceconsists of a switch 1516 which permits a selection of either one of theresistances 1503 and 1504, the value of the resistance selecteddetermining the effective sensitivity of phototransistor 1502 and,therefore, the device sensitivity.

In FIG. 16 there is shown a scale device intended for permitting anexternal regulation of the sensitivity, i.e., related to focal distance,or range, and/or diaphragm apertures. Moreover, we have combined thisdevice with the usual focal distance aperture calculator of electronicphotofiashes and with other improvements as well. This regulating deviceconsists of a fixed interchangeable disc 1601 and a rotatable andselflocking disc 1604 coupled to the device for regulating thesensitivity of the control device.

Graduated in degrees DIN, scale 1603 on disc 1601 is provided forsetting'the film sensitivity, and graduated in meters, scale 1602 isprovided for setting distances. In the case of a photographic camerafitted with an adjustable diaphragm, the disc 1604 is to be rotated soas to bring the desired aperture indication on scale 1607 right oppositethe sensitivity figure on scale 1603 for the film being utilized. Thezone 1605 of disc 1604 shows on scale 1602 the range of distances forwhich the control device will work accurately.

Another way of using this same device is to select the focal distance,or range, and read the aperture to be used opposite the sensitivityfigure for the film being used.

' For use with a photographic camera fitted with a fixed diaphragm, asfor example the Minox camera with a 3.5 aperture, the disc 1604 isrotated so as to bring the Minox" pointer 1609 oppositethe sensitivityfor the film being used on scale 1603. The zone 1605 of the disc 1604shows on scale 1602 the range of distances for which the control devicecan work accurately.

If the control device is not to be used, one must rotate the disc 1604so as to bring the NA pointer (=nonautomatic) 1606 opposite thesensitivity figure of the film used on scale 1603.

The scales 1608 and 1602 are used in the same manner as those of acustomary distance aperture calculator. This operation resultsin'setting the control device sensitivity to the starting, or zeropoint, which means that it is out of action.

This device may advantageously be combined with a light source 1610which allows easier use and reading.

The same device may also be combined with the following luminousindicators:

for the charge of the photoflash capacitor 1611;

for the control device, to indicate whether it functions or not,(functioning 1612, not functioning 1613);

for the achievement of the functioning of the control device 1614.

FIG. 17 shows essentially the same device as FIG. 16, but the device ofFIG. 17 is in the shape of a fixed and interchangeable guide strip 1701and a sliding and selflocking slider 1704.

In FIG. 18 there is shown a control device which is fundamentallyidentical to that of FIG. 15, but equipped for manual regulation. Inthis case, the light sensor is replaced by a variable resistance 1801whose setting determines the period required for the capacitor 1802 ofthe integrator to reach its triggering charge.

In FIG. 19 there is shown an optical control and indicator device foroperating the control device. This optical device consists of afiber-optic element 1902 one end of which is placed on the special arcarrester 1901 which emits light when actuated. The other end of the Iregulation scale unit.

Possibly, a complementary optical system 1904 can be used to furtherincrease the visibility of this indicator.

In FIG. 20 there is .shown one embodiment of the above-mentioned specialgas-filled tube of the arc arrester type. This consists of anelectrically isolating enclosure 2003, which can be transparent,translucent or opaque, whose interior 2005 is filled with a gas,preferably argon and contains two preferably identical and unpolarizedelectrodes 2001 and 2002. A third firing electrode 2006 is arrangedoutside the enclosure 2003 and is extended by the connecting wire 2007.The electrodes 2001 and 2002 are located and formed in such a way, andthe filling and the pressure of the gas are chosen in such a manner,that this tube will function to perform an arc operation. The modifiedembodiment of FIG. 21. has a firing electrode 2106 which protrudes intothe gas-filled interior 2105 of the enclosure 2103.

As can be seen from FIGS. 20a and 21a, which show modified embodimentsof the devices of FIGS. 20 and 21, the enclosures 2003 and 2103 areformed in the shape of tubes and are delimited by two electrodes of thesocket" type, and oflarge surface area. The length of this tube is aboutthe same as its diameter.

It will be understood that the above description of the presentinvention is susceptible to various modifications, changes andadaptations, and the same are intended to be comprehended within themeaning and range of equivalents of the appended claims.

We claim:

I. In a device for controlling the operation of an element whichconverts an electric current into a light flash and including a storagecapacitor storing energy for supplying the element, a light sensorarranged for sensing light produced by the element and reflected from anobject and for producing an electrical output proportional to theintensity of the light which it receives, and an integrator connected toreceive the output from the sensor and to produce a controlsignalrepresenting the time integral of the received light intensity, theimprovement comprising an electronic switch having two main electrodesvia which said switch is connected in series between said capacitor andsaid element, and having a control electrode connected to saidintegrator to receive the control signal from said integrator, theapplication of the control signal to said control electrode renderingsaid switch nonconductive and thus opening the circuit between saidcapacitor and said element and halting the discharge of said capacitorfor generally conserving energy from said capacitor when the controlsignal from said integrator reaches a predetermined value.

2. In adevice for controlling the operation of an element which convertsan electric current into a light flash and including a storage capacitorstoring energy for supplying the element, a light sensor arranged forsensing light produced by the element and reflected from an object andfor producing an electrical output proportional to the intensity of thelight which it receives, and an integrator connected to receive theoutput from the sensor and to produce a control signal representing thetime integral of the received light intensity, the improvementcomprising an electronic switch having two main electrodes via whichsaid switch is connected in series between said capacitor and saidelement, and having a control electrode connected to said integrator toreceive the control signal from said integrator, said electronic switchbeing conducting when an electric current is flowing through theelement, and the application of the control signal to said controlelectrode rendering said switch nonconductive and thus opening thecircuit between said capacitor and said element and halting thedischarge of said capacitor for generally conserving energy from saidcapacitor when the control signal from said integrator reaches apredetermined value.

3 An arrangement as defined in claim 2 wherein said electronic switch iscomposed of a semiconductor element. r I

4. An arrangement as defined in claim 3 wherein said semiconductorelement is constituted by a gate turn off switch.

5. In a device for controlling the operation of an element whichconverts an electric current into a light flash and including a storagecapacitor storing energy for supplying the element, a light sensorarranged for sensing light produced by the element and reflected from anobject and for producing an electrical output proportional to theintensity of the light which it receives, and an integrator connected toreceive the output from the sensor and to produce a control signalrepresenting the time integral of the received light intensity, theimprovement comprising a normally conducting electronic switch havingtwo main electrodes via which said switch is connected in series betweensaid capacitor and said element, and having a control electrodeconnected tosaid integrator to receive the control signal from saidintegrator, the application of the control signal to said controlelectrode rendering said switch nonconductive and thus opening thecircuit between said capacitor and said element and halting thedischarge of said capacitor when the control signal from said integratorreaches a predetermined value.

6. In a device for controlling the operation of an element whichconverts an electric current into a light flash and including a storagecapacitor storing energy for supplying the element, a light sensorarranged for sensing light produced by the element and reflected.

from an object and for producing an electrical output proportional tothe intensity of the light which it receives, and an integratorconnected to receive the out-' put from the sensor and to produce acontrol signal representing the time integral of the received lightintensity, the improvement comprising an electronic gate turn off switchhaving two main electrodes via which said switch is connected in seriesbetween said capacitor and said element, and having a control electrodeconnected to said integrator to receive the control signal from saidintegrator, the application of the control signal to said controlelectrode rendering said switch nonconductive and thus opening thecircuit between said capacitor and said element and halting thedischarge of said capacitor when the control signal from said integratorreaches a predetermined value.

7. A control circuit for controlling the operation of flash tube meanswherein electrical energy is supplied to said tube means from a supplysource for causing said tube means to emit a light flash and wherein thepassage of current through said tube means is controllable forconserving energy of the supply source, said control circuit comprisinga supply source,

electronic switch means having a pair of main current carryingelectrodes, and having a control electrode for receiving an electricalsignal for rendering said switch means conductive,

biasing means connected to normally apply a biasing voltage across saidswitch means when said switch is in its nonconductive state, circuitmeans coupling the main electrodes of said switch means in series withsaid tube means and said supply source to enable, when said switch meansis rendered conductive, passage of current between said pair of maincurrent carrying electrodes to cause ionization of said tube meanswhereby generation of a light flash therefrom occurs, and

control means coupled with said electronic switch means and responsiveto light sensing means to render said electronic switch meansnonconductive and cause termination of said light.

8. A circuit as in claim 7 wherein said biasing means includes voltagedivider means coupled with said switch means for normally applying abiasing voltage across the main electrodes of said switch means.

9. A circuit as defined in claim 7 wherein said control means includes asecond electronic switch means coupled with said first-named electronicswitch means and coupled with light sensing means for sensing lightemitted by said lamp means for causing reversal in the polarity of thevoltage across the main electrodes of said first-named switch means uponreceipt by said light sensing means of a predetermined amount of light.

10. A circuit as in claim 9 wherein said second switch means comprises agas-filled tube having two main electrodes and'a firing electrode, saidfiring electrode being responsive to said light sensing means.

11. A circuit as in claim 9 wherein each of said electronic switch meanscomprises a thyristor.

12. A circuit for controlling the operation of a load element whichconverts an electric current from a supply source into a light flash andwhich is operatively associated with means for sensing the lightproduced by the element and producing a signal when a predeterminedquantity of light has been produced, said circuit comprising, incombination:

electronic switch means having a pair of main current carryingelectrodes by which it is connected in se ries between the load elementand the supply source, said switchmeans being electrically coupled withtriggering means of said load element and having a controlelectrode forreceiving an electrical signal which renders said switch meansconductive for passing current therethrough to said triggering means .tocause said load element to ionize whereby a light flash is produced; andflash terminating means connected between said sensing means and saidswitch means for rendering said switch means nonconductive upon theproduction of a signal by said sensing means, to cause termination ofthe light flash and generally conserve energy of said supply source. 713. An arrangement as defined in claim 12 wherein said triggering meanscomprises a trigger transformer and energy source electrically connectedto said switch means.

14. A circuit for controlling the operation of a load element whichconverts an electric current from a supply source into a light flash andwhich is'operatively associated with means for sensing the lightproduced by the element and producing a signal when a predeterminedquantity of light has been produced, said circuit comprising, incombination:

electronic switch means having a pair of main current carryingelectrodes by which it is connected in series between the load elementand the supply source, said switch means being electrically connectedwith triggering means of said load element for passing current to saidtriggering means for ionizing said load element whereby a light flash isproduced by said load element; and

flash terminating means connected between said sensing means and saidswitch means for rendering said switch means nonconductive upon theproduction of a signal by said sensing meansto terminate the light flashand generally conserve energy of said supply source.

15. A circuit for controlling the operation of a load element whichconverts an electric current from a supply source into a light flash andwhich is operatively associated with means for sensing the lightproduced by the element and producing a signal when a predeterminedquantity of light has been produced, said circuit comprising, inc0mbination:

a load element comprising a flash lamp and trigger means therefor;

electronic switch means having a pair of main current carryingelectrodes by which it is connected in series between the load elementand the supply source, said switch means being electrically coupled withsaid flash lamp and said trigger means, and the conduction of currentthrough said switch means causing both said trigger means to ionize saidlamp and said lamp to generate a light flash; and

flash terminating means connected with light sensing means and saidswitch means for rendering said switch means nonconductive upon theproduction of a signal by said light sensing means to terminate thelight flash from said lamp and enableconservation of energy of saidsupply source.

16. A circuit for controlling the operation of a load elementwhich'converts an electric current from a supply source into a lightflash and which is operatively associated with means for sensing thelight produced by the element and producing a signal when apredetermined quantity of light has been produced, said circuitcomprising, in combination:

first electronic switch means having a pair of main current carryingelectrodes by which it is connected in series between the load elementand the supply source, said switch means having biasing means coupledtherewith to apply voltage across the switch means when said switchmeans is nonconductive, and having a control electrode for receiving anelectrical signal for rendering said switch means conductive for passingelectrical current therethrough to ionize said load element whereby saidload element produces a light flash;

second electronic switch means having two main electrodes and a controlelectrode; means connecting one main electrode of said second electronicswitch means to one of said main electrodes of said first electronicswitch means, and means connecting the other main electrode of saidsecond electronic switch means to a voltage source; and v said controlelectrode of said second electronic switch means being connected to saidlight sensing means for receiving the electrical signal produced therebyto render said second switch means conductive for supplying a voltage ata main electrode of said first switch means which reverses the polarityof the voltage across the main electrodes of said first switch means andthus renders said first switch means nonconductive to cause terminationof the light flash for generally conserving energy of said supplysource. 17. A circuit as defined in claim. 16 wherein said secondelectronic switch means is constituted by a gasfilled tube having twomain electrodes and one firing electrode and constructed to operate byproducing an arc.

18. A circuit for controlling the operation of a load element whichconverts an electric current from a supply source into a light flash andwhich is operatively associated with means for sensing the lightproduced by the element and producing a signal when a predeterminedquantity of light has been produced, said circuit comprising, incombination:

first electronic switch means having a pair of main current carryingelectrodes by which it is connected in series between the load elementand the supply source, means establishing a voltage across said switchmeans when said switch means is nonconductive, and said switch meanshaving a control electrode coupled in series with a voltage source andsynchronization contact means for receiving an electrical signal whichrenders said switch means conductive for applying electrical energy tosaid load element for producing a light flash;

second electronic switch means having two main electrodes and a controlelectrode;

means connecting one main electrode of said second electronic switchmeans to one of said main electrodes of said first electronic switchmeans, and means connecting the other main electrode of said secondelectronic switch means to a voltage source;

said control electrode of said second electronic switch means beingconnected to said light sensing means for receiving the electricalsignal produced thereby to render said second switch means conductivefor supplying a voltage at a main electrode of said first switch meanswhich reverses the polarity of the voltage across the main electrodes ofsaid first switch means and thus renders said first switch meansnonconductive to cause termination of the light flash for generallyconserving energy of said supply source; and

inductance means in series with said load element and said firstelectronic switch means for modifying the current impulse to said loadelement. 19. A circuit as defined in claim 18 wherein said secondelectronic switch comprises a gas-filled tube having two main electrodesand a firing electrode, said firing electrode being responsive to saidlight sensing means.

20. A circuit for controlling the operation of a load element whichconverts an electric current from a supply source into a light flash andwhich is operatively associated with means for sensing the lightproduced by the element and producing a signal when a predeterminedquantity of light has been produced, said circuit comprising, incombination:

first electronic switch means having a pair of main current carryingelectrodes by which it is connected in series between the load elementand the supply source and having a control electrode for receiving anelectrical signal which renders said switch conductive for applyingelectrical energy to said load element for producing a light flash;

second electronic switch means having two main electrodes and a controlelectrode; and

means connecting one main electrode of said second electronic switchmeans to one of said main electrodes of said first electronic switchmeans, and means connecting the other main electrode of said secondelectronic switch means to a voltage source; said control electrode ofsaid second electronic switch means being connected to said lightsensing means for receiving the electrical signal produced thereby torender said second switch means conductive for supplying a voltage at amain electrode of said first switch means which reverses the polarity ofthe voltage across the main electrodes of said first switch means andthus renders said first switch means nonconductive to cause terminationof the light flash for generally conserving energy of said supplysource;

said load element having a trigger input which initiates the convertingof an electric current from the supply source into a light flash when asignal is applied to the trigger input, and said first electronic switchmeans being connected with both the load element and said trigger inputfor enabling current flow through the first electronic switch means tocause the trigger input to ionize the load element and enable the loadelement to generate a light flash.

circuit means connecting said electronic switch I means with said flashtube means and said supply source, said circuit means connecting themain 1 electrodes of said switch means in series with said tube meansand said supply source and including biasing means for establishing avoltage across said switch means when said switch means isnonconductive, and including means for applying a signal to said controlelectrode to render said switch means conductive for (a) enablingcurrent flow between said pair of main current carrying electrodesbefore said flash tube means ionizes and (b) causing a light flash tobe' generated by said tube means, and

control means coupled with said electronic switch means and responsiveto light sensing means to render said electronic switch meansnonconductive and cause termination of said light flash.

22. A control circuit as in claim 21 wherein said flash tube meansincludes a flash tube and trigger means therefor, and

said circuit means includes means coupling said switch means in serieswith both said tube and trigger means, and said biasing means includesvoltage divider means coupled with the main electrodes of said switchmeans for establishing said voltage across said switch means.

23. A circuit for controlling the operation of a load element whichconverts an electric current from a supply source into a light flash andwhich is operatively associated with means for sensing the lightproduced by the element and producing a signal when a predeterminedquantity of light has been produced, said circuit comprising, incombination:

first electronic switch means having a pair of main current carryingelectrodes by which it is connected in series between the load elementand the supply source, and having a control electrode for receiving anelectrical signal which renders said switch means conductive forapplying electrical energy to said load element for producing a light,

a gas-filled tube having two closely spaced main electrodes and onefiring electrode and operative as a switch,

means connecting one main electrode of said gasfilled tube to one ofsaid main electrodes of said first electronic switch means, andcommutating capacitor means connected between said other main electrodeof said gas-filled tube and the junction of said first electronic switchmeans and said load element;

an inductance coil connected in series between said source and saidfirst electronic switch means and said gas-filled tube means forreducing current impulses thereto; and

said control electrode of said gas-filled tube being connected to lightsensing means for receiving the electrical signal produced thereby torender said gas-filled tube conductive for supplying a voltage at a mainelectrode of said first switch means which reverses the polarity of thevoltage across the main electrodes of said first switch means and thusrenders said first switch means nonconductive to cause termination ofthe light flash from said load element to generally conserve energy ofsaid supply SOUI'CC.

1. In a device for controlling the operation of an element whichconverts an electric current into a light flash and including a storagecapacitor storing energy for supplying the element, a light sensorarranged for sensing light produced by the element and reflected from anobject and for producing an electrical output proportional to theintensity of the light which it receives, and an integrator connected toreceive the output from the sensor and to produce a control signalrepresenting the time integral of the received light intensity, theimprovement comprising an electronic switch having two main electrodesvia which said switch is connected in series between said capacitor andsaid element, and having a control electrode connected to saidintegrator to receive the control signal from said integrator, theapplication of the control signal to said control electrode renderingsaid switch nonconductive and thus opening the circuit between saidcapacitor and said element and halting the discharge of said capacitOrfor generally conserving energy from said capacitor when the controlsignal from said integrator reaches a predetermined value.
 2. In adevice for controlling the operation of an element which converts anelectric current into a light flash and including a storage capacitorstoring energy for supplying the element, a light sensor arranged forsensing light produced by the element and reflected from an object andfor producing an electrical output proportional to the intensity of thelight which it receives, and an integrator connected to receive theoutput from the sensor and to produce a control signal representing thetime integral of the received light intensity, the improvementcomprising an electronic switch having two main electrodes via whichsaid switch is connected in series between said capacitor and saidelement, and having a control electrode connected to said integrator toreceive the control signal from said integrator, said electronic switchbeing conducting when an electric current is flowing through theelement, and the application of the control signal to said controlelectrode rendering said switch nonconductive and thus opening thecircuit between said capacitor and said element and halting thedischarge of said capacitor for generally conserving energy from saidcapacitor when the control signal from said integrator reaches apredetermined value.
 3. An arrangement as defined in claim 2 whereinsaid electronic switch is composed of a semiconductor element.
 4. Anarrangement as defined in claim 3 wherein said semiconductor element isconstituted by a gate turn off switch.
 5. In a device for controllingthe operation of an element which converts an electric current into alight flash and including a storage capacitor storing energy forsupplying the element, a light sensor arranged for sensing lightproduced by the element and reflected from an object and for producingan electrical output proportional to the intensity of the light which itreceives, and an integrator connected to receive the output from thesensor and to produce a control signal representing the time integral ofthe received light intensity, the improvement comprising a normallyconducting electronic switch having two main electrodes via which saidswitch is connected in series between said capacitor and said element,and having a control electrode connected to said integrator to receivethe control signal from said integrator, the application of the controlsignal to said control electrode rendering said switch nonconductive andthus opening the circuit between said capacitor and said element andhalting the discharge of said capacitor when the control signal fromsaid integrator reaches a predetermined value.
 6. In a device forcontrolling the operation of an element which converts an electriccurrent into a light flash and including a storage capacitor storingenergy for supplying the element, a light sensor arranged for sensinglight produced by the element and reflected from an object and forproducing an electrical output proportional to the intensity of thelight which it receives, and an integrator connected to receive theoutput from the sensor and to produce a control signal representing thetime integral of the received light intensity, the improvementcomprising an electronic gate turn off switch having two main electrodesvia which said switch is connected in series between said capacitor andsaid element, and having a control electrode connected to saidintegrator to receive the control signal from said integrator, theapplication of the control signal to said control electrode renderingsaid switch nonconductive and thus opening the circuit between saidcapacitor and said element and halting the discharge of said capacitorwhen the control signal from said integrator reaches a predeterminedvalue.
 7. A control circuit for controlling the operation of flash tubemeans wherein electrical energy is supplied to said tube means from asupply source foR causing said tube means to emit a light flash andwherein the passage of current through said tube means is controllablefor conserving energy of the supply source, said control circuitcomprising a supply source, electronic switch means having a pair ofmain current carrying electrodes, and having a control electrode forreceiving an electrical signal for rendering said switch meansconductive, biasing means connected to normally apply a biasing voltageacross said switch means when said switch is in its nonconductive state,circuit means coupling the main electrodes of said switch means inseries with said tube means and said supply source to enable, when saidswitch means is rendered conductive, passage of current between saidpair of main current carrying electrodes to cause ionization of saidtube means whereby generation of a light flash therefrom occurs, andcontrol means coupled with said electronic switch means and responsiveto light sensing means to render said electronic switch meansnonconductive and cause termination of said light.
 8. A circuit as inclaim 7 wherein said biasing means includes voltage divider meanscoupled with said switch means for normally applying a biasing voltageacross the main electrodes of said switch means.
 9. A circuit as definedin claim 7 wherein said control means includes a second electronicswitch means coupled with said first-named electronic switch means andcoupled with light sensing means for sensing light emitted by said lampmeans for causing reversal in the polarity of the voltage across themain electrodes of said first-named switch means upon receipt by saidlight sensing means of a predetermined amount of light.
 10. A circuit asin claim 9 wherein said second switch means comprises a gas-filled tubehaving two main electrodes and a firing electrode, said firing electrodebeing responsive to said light sensing means.
 11. A circuit as in claim9 wherein each of said electronic switch means comprises a thyristor.12. A circuit for controlling the operation of a load element whichconverts an electric current from a supply source into a light flash andwhich is operatively associated with means for sensing the lightproduced by the element and producing a signal when a predeterminedquantity of light has been produced, said circuit comprising, incombination: electronic switch means having a pair of main currentcarrying electrodes by which it is connected in series between the loadelement and the supply source, said switch means being electricallycoupled with triggering means of said load element and having a controlelectrode for receiving an electrical signal which renders said switchmeans conductive for passing current therethrough to said triggeringmeans to cause said load element to ionize whereby a light flash isproduced; and flash terminating means connected between said sensingmeans and said switch means for rendering said switch meansnonconductive upon the production of a signal by said sensing means, tocause termination of the light flash and generally conserve energy ofsaid supply source.
 13. An arrangement as defined in claim 12 whereinsaid triggering means comprises a trigger transformer and energy sourceelectrically connected to said switch means.
 14. A circuit forcontrolling the operation of a load element which converts an electriccurrent from a supply source into a light flash and which is operativelyassociated with means for sensing the light produced by the element andproducing a signal when a predetermined quantity of light has beenproduced, said circuit comprising, in combination: electronic switchmeans having a pair of main current carrying electrodes by which it isconnected in series between the load element and the supply source, saidswitch means being electrically connected with triggering means of saidload element for passing current to said triggering means for ionizingsaid load eleMent whereby a light flash is produced by said loadelement; and flash terminating means connected between said sensingmeans and said switch means for rendering said switch meansnonconductive upon the production of a signal by said sensing means toterminate the light flash and generally conserve energy of said supplysource.
 15. A circuit for controlling the operation of a load elementwhich converts an electric current from a supply source into a lightflash and which is operatively associated with means for sensing thelight produced by the element and producing a signal when apredetermined quantity of light has been produced, said circuitcomprising, in combination: a load element comprising a flash lamp andtrigger means therefor; electronic switch means having a pair of maincurrent carrying electrodes by which it is connected in series betweenthe load element and the supply source, said switch means beingelectrically coupled with said flash lamp and said trigger means, andthe conduction of current through said switch means causing both saidtrigger means to ionize said lamp and said lamp to generate a lightflash; and flash terminating means connected with light sensing meansand said switch means for rendering said switch means nonconductive uponthe production of a signal by said light sensing means to terminate thelight flash from said lamp and enable conservation of energy of saidsupply source.
 16. A circuit for controlling the operation of a loadelement which converts an electric current from a supply source into alight flash and which is operatively associated with means for sensingthe light produced by the element and producing a signal when apredetermined quantity of light has been produced, said circuitcomprising, in combination: first electronic switch means having a pairof main current carrying electrodes by which it is connected in seriesbetween the load element and the supply source, said switch means havingbiasing means coupled therewith to apply voltage across the switch meanswhen said switch means is nonconductive, and having a control electrodefor receiving an electrical signal for rendering said switch meansconductive for passing electrical current therethrough to ionize saidload element whereby said load element produces a light flash; secondelectronic switch means having two main electrodes and a controlelectrode; means connecting one main electrode of said second electronicswitch means to one of said main electrodes of said first electronicswitch means, and means connecting the other main electrode of saidsecond electronic switch means to a voltage source; and said controlelectrode of said second electronic switch means being connected to saidlight sensing means for receiving the electrical signal produced therebyto render said second switch means conductive for supplying a voltage ata main electrode of said first switch means which reverses the polarityof the voltage across the main electrodes of said first switch means andthus renders said first switch means nonconductive to cause terminationof the light flash for generally conserving energy of said supplysource.
 17. A circuit as defined in claim 16 wherein said secondelectronic switch means is constituted by a gas-filled tube having twomain electrodes and one firing electrode and constructed to operate byproducing an arc.
 18. A circuit for controlling the operation of a loadelement which converts an electric current from a supply source into alight flash and which is operatively associated with means for sensingthe light produced by the element and producing a signal when apredetermined quantity of light has been produced, said circuitcomprising, in combination: first electronic switch means having a pairof main current carrying electrodes by which it is connected in seriesbetween the load element and the supply source, means establishing avoltage across said switch means whEn said switch means isnonconductive, and said switch means having a control electrode coupledin series with a voltage source and synchronization contact means forreceiving an electrical signal which renders said switch meansconductive for applying electrical energy to said load element forproducing a light flash; second electronic switch means having two mainelectrodes and a control electrode; means connecting one main electrodeof said second electronic switch means to one of said main electrodes ofsaid first electronic switch means, and means connecting the other mainelectrode of said second electronic switch means to a voltage source;said control electrode of said second electronic switch means beingconnected to said light sensing means for receiving the electricalsignal produced thereby to render said second switch means conductivefor supplying a voltage at a main electrode of said first switch meanswhich reverses the polarity of the voltage across the main electrodes ofsaid first switch means and thus renders said first switch meansnonconductive to cause termination of the light flash for generallyconserving energy of said supply source; and inductance means in serieswith said load element and said first electronic switch means formodifying the current impulse to said load element.
 19. A circuit asdefined in claim 18 wherein said second electronic switch comprises agas-filled tube having two main electrodes and a firing electrode, saidfiring electrode being responsive to said light sensing means.
 20. Acircuit for controlling the operation of a load element which convertsan electric current from a supply source into a light flash and which isoperatively associated with means for sensing the light produced by theelement and producing a signal when a predetermined quantity of lighthas been produced, said circuit comprising, in combination: firstelectronic switch means having a pair of main current carryingelectrodes by which it is connected in series between the load elementand the supply source and having a control electrode for receiving anelectrical signal which renders said switch conductive for applyingelectrical energy to said load element for producing a light flash;second electronic switch means having two main electrodes and a controlelectrode; and means connecting one main electrode of said secondelectronic switch means to one of said main electrodes of said firstelectronic switch means, and means connecting the other main electrodeof said second electronic switch means to a voltage source; said controlelectrode of said second electronic switch means being connected to saidlight sensing means for receiving the electrical signal produced therebyto render said second switch means conductive for supplying a voltage ata main electrode of said first switch means which reverses the polarityof the voltage across the main electrodes of said first switch means andthus renders said first switch means nonconductive to cause terminationof the light flash for generally conserving energy of said supplysource; said load element having a trigger input which initiates theconverting of an electric current from the supply source into a lightflash when a signal is applied to the trigger input, and said firstelectronic switch means being connected with both the load element andsaid trigger input for enabling current flow through the firstelectronic switch means to cause the trigger input to ionize the loadelement and enable the load element to generate a light flash.
 21. Acontrol circuit for controlling the operation of flash tube meanswherein electrical energy is supplied to said tube means from a supplysource for causing said tube means to emit a light flash and wherein thepassage of current through said tube means is controllable forconserving energy of the supply source, said control circuit comprisinga supply source, electronic switch means having a paiR of main currentcarrying electrodes and a control electrode, circuit means connectingsaid electronic switch means with said flash tube means and said supplysource, said circuit means connecting the main electrodes of said switchmeans in series with said tube means and said supply source andincluding biasing means for establishing a voltage across said switchmeans when said switch means is nonconductive, and including means forapplying a signal to said control electrode to render said switch meansconductive for (a) enabling current flow between said pair of maincurrent carrying electrodes before said flash tube means ionizes and (b)causing a light flash to be generated by said tube means, and controlmeans coupled with said electronic switch means and responsive to lightsensing means to render said electronic switch means nonconductive andcause termination of said light flash.
 22. A control circuit as in claim21 wherein said flash tube means includes a flash tube and trigger meanstherefor, and said circuit means includes means coupling said switchmeans in series with both said tube and trigger means, and said biasingmeans includes voltage divider means coupled with the main electrodes ofsaid switch means for establishing said voltage across said switchmeans.
 23. A circuit for controlling the operation of a load elementwhich converts an electric current from a supply source into a lightflash and which is operatively associated with means for sensing thelight produced by the element and producing a signal when apredetermined quantity of light has been produced, said circuitcomprising, in combination: first electronic switch means having a pairof main current carrying electrodes by which it is connected in seriesbetween the load element and the supply source, and having a controlelectrode for receiving an electrical signal which renders said switchmeans conductive for applying electrical energy to said load element forproducing a light flash; a gas-filled tube having two closely spacedmain electrodes and one firing electrode and operative as a switch,means connecting one main electrode of said gas-filled tube to one ofsaid main electrodes of said first electronic switch means, andcommutating capacitor means connected between said other main electrodeof said gas-filled tube and the junction of said first electronic switchmeans and said load element; an inductance coil connected in seriesbetween said source and said first electronic switch means and saidgas-filled tube means for reducing current impulses thereto; and saidcontrol electrode of said gas-filled tube being connected to lightsensing means for receiving the electrical signal produced thereby torender said gas-filled tube conductive for supplying a voltage at a mainelectrode of said first switch means which reverses the polarity of thevoltage across the main electrodes of said first switch means and thusrenders said first switch means nonconductive to cause termination ofthe light flash from said load element to generally conserve energy ofsaid supply source.